An MR read transducer requires an active region and passive regions. The active region comprises suitable means for transversely biasing the transducer, and each passive region generally includes suitable means for longitudinally biasing the transducer.
The longitudinal bias is necessary to free the MR transducer from Barkhausen noise. This longitudinal bias can be provided by a "patterned exchange" which uses either an antiferromagnetic or a hard magnetic biasing layer that is exchange-coupled to the passive regions to induce a single magnetic domain state in the active region.
Commonly assigned U.S. Pat. No. 4,663,685 describes a simple implementation of patterned exchange using a continuous spacer layer. This patent discloses an MR transducer comprising a continuous spacer layer separating a continuous MR layer and a continuous soft magnetic layer. Anti-ferromagnetic bias material deposited only in the passive end regions produces a bias field which is directed longitudinally of the transducer. Because the magnetic orientation of the soft magnetic layer in the passive regions is not controlled by the exchange coupling, multiple magnetic states are possible. Tests of head disk assemblies (HDAs) show occasional problems because the magnetic fields generated by the passive regions influence the MR response of the transducer.
Commonly assigned U.S. Pat. No. 4,785,366 shows a patterned spacer layer configuration that was developed to provide direct control, by exchange coupling, of the entire passive regions to produce optimium transducer performance. This patent discloses an MR transducer comprising a patterned spacer layer between a continuous soft magnetic layer and a continuous MR layer, and an exchange bias layer of antiferromagnetic material overlaying the soft magnetic layer. The spacer layer extends beyond the active region into the adjacent ends of the passive end regions to provide alignment tolerance during fabrication.
It has been found during manufacture and testing at the HDA level, however, that some patterned spacer configured transducers have been unstable as denoted by waveform distortions. It was also found that these transducers often exhibited considerable variability in output characteristics even if processed from the same wafer row. Both the instabilities and some of the performance variations of the patterned spacer configuration were found to originate within the regions of unconstrained moment in the soft magnetic film that correspond to the regions in which the spacer layer extends beyond the central active region into the two passive end regions. No correlation with process variations were found to account for these random occurrences of instability.
Since no process solution appears possible, there is a need for a solution that can be achieved by a configuration change that will increase the tolerable range of normal material and manufacturing process variations in a manner which does not complicate the fabrication process and maintains high yields.
No prior art known to applicants discloses or suggests an MR transducer of either the continuous spacer or the patterned spacer configuration having a canted exchange field in the passive end regions to match the magnetic moment between the central active region and the passive end regions during reading; i.e., during operation when the current is on. In prior arrangements, the orientation of the passive region remained the same whether the current was on or off and the moment was matched when the current was off, rather than when the current was on.